Conventionally, an impact wrench configured to firmly tighten bolts and nuts with the primary hammer and the secondary hammer while mitigating vibrations in the axial direction without weakening the rotary impact force is known (see, for example, JP 4457170 B).
With the conventional impact wrench disclosed in JP 4457170 B, two configurations are disclosed, namely, a first configuration and a second configuration, as a structure for preventing so-called “precession rotation”, in which the rotational axis of the secondary hammer gyrates about the rotational axis of the spindle.
The conventional first configuration is designed to prevent precession rotation by setting the inner diameter of a hole formed in the center of the bottom of the secondary hammer to substantially the same size as the outer diameter of spindle (see FIG. 1 of JP 4457170 B).
Furthermore, the conventional second configuration is designed to prevent precession rotation by supporting a ball bearing for the spindle and a ball bearing for the secondary hammer with a single cylindrical bush that serves as a spacer (see FIG. 5 of JP 4457170 B).